Apparatus for cooling a high-speed missile



May 15, 1962 C. J. HIRSCH v APPARATUS FOR COOLING A HIGH-SPEED MISSILE Filed June 6, 1958 United States This invention relates to the cooling of a high-speed missile and, more specifically, to apparatus utilizing the principle of thermionic emission to stabilize the temperature of the missile surface at some predetermined temperature, particularly while the missile is in the earths atmosphere.

An object of this invention is to provide a missile capable of traveling at high speeds through the atmosphere Without disintegrating.

Another object of this invention is to provide a missile with its surface cooled by the principle of thermionic emission.

Another object of this invention is to provide in a missile apparatus for cooling its surface by the principle of thermionic emission.

A further object of the invention is to provide in a missile apparatus for maintaining thermionic emission from the missile surface during the P riod of time in which it is desired to cool the missile.

In accordance with the present invention, there is provided apparatus for cooling a high-speed missile comprising a missile surface capable of thermionic emission substantially commencing when the missile surface reaches a high temperature caused by air friction. The apparatus further includes means electrically connected to the missile surface for neutralizing the positive charge accumulating on the surface by the action of the electron emission.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, there is shown therein a missile incorporating a representative embodiment of the invention. The drawing is not to scale.

A missile 10 constructed in accordance with the present invention includes a thermionic emitting surface for cooling the missile. The surface 11 may be a layer of material, as for instance tungsten, which encompasses at least that portion of the missile desired to be cooled.

The actual preferred properties and thickness of this material are determined in a manner more fully explained hereinafter; however, in the case of a layer of. tungsten, the thickness may be of the order of 0.08 inch.

To enable the electron emission to continue at the desired rate for any length of time, the apparatus also includes means electrically coupled to the missile surface for discharging i.e., neutralizing or eliminating, the positive charge accumulating on the surface by the action of the electron emission. Included in this means is apparatus for generating fine, chargeable particles and passing them through a fine mesh screen 18 which is electrically connected to the missile surface 11. Suitable particles would consist of carbon dust such as would be developed from a controlled partial burning of oil. The apparatus, as illustrated, includes tank 12 containing gases such as oxygen mixed with nitrogen under high pressure and retained therein by a normally closed valve 13. This apparatus further includes tank 14 containing a combustible 'oil under high, pressure and simiatent larly held therein by normally closed valve 15. Valves 13 and 15 are coupled to solenoid 26. These tanks are coupled to the common channel 16 wherein there is located a conventional electrically operated igniter 25. The channel 16 continues past the iguiter, through the missile surface, where it flares out the exit aperture 17 which is funnel-shaped. Across the aperture (and covering the entire area of the aperture) is a fine mesh screen 18 surrounding a diffusing device 19, which latter device is centered in the aperture 17. The screen 13 is included so that the only exit from channel 16 is through the holes of the screen which are sufiiciently small so that substantially all the chargeable particles passing therethrough will assume the potential of the missile surface in a manner more fully explained hereinafter. To this end the screen 18 is electrically connected through the wall 20 of the missile to the thermionic emitting surface 11.

Also included in the said apparatus is a block 21, located at the surface of the missile 10 preferably in its frontal area. This block is preferably of a material designed to disintegrate at a temperature which is equal to or slightly less than the temperature at which substantial thermionic emission occurs from surface 11. A relay contact 22 is held in a normally open position by spring 23 resting against block 21. A source of voltage 24 is coupled to igniter 25 through the normally open relay contact 22. Solenoid 26 is also connected to voltage source 24 through the normally open relay contact 22. This foregoing portion of the missile including units 21-26, inclusive, comprises a triggering mechanism for preventing ejection of the chargeable particles until such action is required to maintain cooling of the missile.

Before explaining the operation of the thermionically cooled missile, a brief outline of the problem concerned will be considered. It is well known that missiles traveling through the atmosphere become heated to very high temperatures caused by air friction. The problem is especially important when a missile re-enters the atmosphere after traveling through the space outside of the atmosphere. Thus, at Mach l0 (10 times the speed of sound) this temperature may reach 3800 C. and at Mach 15 (15 times the speed of sound) it may reach 8500 C. At present there are no materials capable of withstanding these temperatures. Therefore, it becomes necessary to effectively cool these missiles to some more reasonable temperature such as 3500 K. A specificillustration of a method of solving this problem will now be considered.

Thermionic emission cools the cathodes of vacuum tubes because, by the emission, power is removed from the cathode equal to the current times the work function. The emission of negative electrons leaves the cathode positively charged With theresult that the emission would stop if there were no means of neutralizing or removing this charge. I

It is known that supersonic aircraft can become charged by air friction to 500,000 volts. Thismeans that the air (which is effectively a high-speed wind passing the missile) is able to remove electrons from the missile against this voltage. For supersonic missiles, this voltage is probably much higher. Therefore the emission would proceed until the missile attains a charge of at least 500,000 volts, and the emission would stabilize to a value of current equal to the ability of the wind to carry off electrons. In the representative embodiment of the invention, the abovementioned charge on the missile is neutralized by the throwing olf of a quantity of very fine particles capable of being charged to the voltage of the missile. Each of these particles, when chargedto 500,000 volts, will carry screen 18. sume the charge appearing thereon. Since the screen is electrically connected to the tungsten surface 11, the' .oi't' a charge equal to 500,000 Q, coulomos, where C is the particle capacity.

Utilizing the thermionic emission equation developed by Dushman, as found at page 281 of'Radio Engineers Handbook, by Terman, 'McGraw-Hill, First Edition, it

can be shown that the emission current density for tungsten at 3500 K. is 220 amps. per square centimeter. The power'emitted can be shown to be 1,000 watts per square c cntimeten'which is equivalent to 240 calories per second per square centimeter. The density of tungsten is 19 grams per cubic centimeter and, assuming a layer thickness of 0.2 cm. (0.08 inch), each square centimeter of the layer oftungsten Weights 318 grams. The specific heat of tungsten'is 0.04 calorie-per gram-degree centig-rade, which means that the heat capacity of the tungsten layer is 0.152 calorie per degree C. per cm. so that a loss of 240 calories per second would cool the missile surface by 240/ 0.l52=l560 C. per second. Theoretically, this emission could continue for the length of time the missile is traveling in the atmosphere except that a positive cm. which is equivalent to 5 10- farads. Each-cubic centimeter of dust holds approximately particles so that each cubic centimeter then has a capacity of a farads. If each particle is charged to 500,000 volts (assuming that to be the potential of the missile surface relative to the surrounding air), then each cubic centimeter carries ofi 500,000X5X 10- =2500 coulombs. To carry oh 220 amps. per square cm., the nussile must throw oif 220+2500-1 cubic cm. of dust per square cm. of missile surface. Therefore, the amount of dust particles necessary to be carried off depends on the size of the missile. If the missile has a surface area of 10,000 cm. the rate of particle discharge necessary to continue the electron emission from the surface would be 0.1 x l0,000=1,000 cm. sec. or approximately 60 ind/sec.

in the operation of the representative embodiment of the invention, when the missile 1 0 heats to a temperature of about 3500 K., the friction developed voltage between the missile surface and the surrounding air'induces substantial electron emission as previously explained. Where it is desired to maintain this emission for an appreciable length of time, the apparatus in the missile is utilized and operates in the following manner The block 21 melts at approximately 3500 K allowing spring 23 to relax,

tliereby closing the contacts of switch 22. When this. happens the voltage from battery 24 is applied simultaneously to the solenoid 25 and igniter 25. 1 Solenoid 26, when activated, opens valves 13 and 15, allowing the gaseous mixture of nitrogen and oxygen from tank 12 to discharge in a controlled flow and to mix with the' combustible oil from tank 14. The new mixture is forced past igniter 25 where'it is burned under controlled conditions to generate a smokecontaining fine carbon particles. then forced out and away from the missile through the The particles passing through the screen ascharge carried ofi by the carbon particles is essentially that samepositive charge accumulated on the surface by the action of. the electron emission. it is for this reason that the soles of the screen 18 should be sufiiciently small The smoke is' to allow substantially all the smoke particles to assume the charge appearing thereon either by actually impinging on the screen or by assuming the charge through other particles actually impinging on the screen.

Other forms of the apparatus may be utilized without having the burning action previously described. For instance, tanl; 12 may contain compressed air and tank 14' may contain fine carbon dust particles with a motor driven impeller blade to throw the dust particles out into the path of the compressed air, whereupon the partciles are forced through screen 18.

Also, it is not necessary that the apparatus and screen be located at therear of the misile. For instance, they may be located in the nose cone of the missile with the dust particles given off and carried back over the missile surface.

The term missile is meant to include all similar devices subject to heating by :air friction because they move through the air at high speed, for example, high-speed aircraft. 7

While there has been described what is at present considered to be the'preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: V p

1. Apparatus for cooling a high-speed missile comprising: a missile surface capable of thermionic emission substantially commencing when the'missile surface reaches a high temperature caused byair friction; and means electrically connected to the missile surface for neutralizing the positive charge accumulating on the surface by the action of the electron emission. g

2. Apparatus for cooling a high-speed missile comprising: a missile surface capable of thermionic emission substantially commencing when the missilesurface reaches a high temperature caused by air friction; and means including a fin mesh screen electrically connected to the missile surface for neutralizing the positive charge accumulating on the surface by the action of the. electron emission. 7 7 j i 3. Apparatus for cooling ahigh-speed missile comprising: a missile surface capable of thermionic emission substantimly commencing when the missile surface reaches a high temperature caused by air friction; and means for neutralizing the positive charge accumulating on the surface by the action of the electron emission and including apparatus forgenerating and ejecting fine [chargeable particles and including afine mesh screen electrically connected to the missile surface and adapted to charge the particles to the surface potential upon their ejection.

4. Apparatus for cooling a high-speed missile comprising: -a missile surface capable of thermionic emission V substantially commencing when the missile surface reaches a high temperature caused by air friction; and means electrically connected to the missile surface for neutralizing the positive charge accumulating on the surface by the action of the electron emission, said means including a triggering mechanism for preventing said neutralizing action until said thermionic emission commences.

5. Apparatus for cooling a high-speed missile comprising: a layer'of material surrounding that portion of the missile desired to be cooled and capable of thermionic emission substantially commencing when the missile surface reaches a high temperature caused by air friction; and means for neutralizing the positive charg so cumulating on the surface by the action of the electron emission and including apparatus for generating and ejecting fine chargeable particles and including a fine mesh screen located in'the ejection path of said particles so as to cause substantial impinging of the particles on said screen at themissile' surface and said screen being 6 Schuler May 14, 1957 Larsen Apr. 21, 1959 electrically connected to the missile surface for charging the particles to the surface potential.

References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS 5 Aviation Week, v01. 68, No. 16, April 1958. A Mc- 2,246,429 Brandt June 17, 1941 Graw Hill publication (page 57 relied on, copy in Scien- 2,468,820 Goddard May 3, 1949 tific Library and Division 10). 

